salutation in parting, also goodbye, good bye, good-by, 1590s, from godbwye (1570s), a contraction of God be with ye (late 14c.), influenced by good-day, good evening, etc. As a noun from 1570s. Intermediate forms in 16c. include God be wy you, God b'uy, God buoye, God buy, etc.

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Definitions of good-bye from WordNet

good-bye (n.)
a farewell remark;
they said their good-byes
Synonyms: adieu / adios / arrivederci / auf wiedersehen / au revoir / bye / bye-bye / cheerio / good-by / goodby / goodbye / good day / sayonara / so long